In a semiconductor manufacture field, there has often been used a plasma processing apparatus which performs an etching process or a film forming process by applying plasma to a target substrate (hereinafter, referred to as “substrate”) such as a silicon wafer. Since such a plasma process has been performed under a depressurized pressure, a vacuum chuck cannot be used to hold the substrate. Thus, there has generally been used a substrate mounting apparatus such as a mechanical clamp or an electrostatic chuck using electrostatic force.
The electrostatic chuck may include a substrate mounting surface made of an insulator having therein an embedded sheet electrode. If a high potential is applied to the sheet electrode, Coulomb force or Johnsen-Rahbek force is generated by static electricity distributed in the insulator and polarized and electrified charges in the substrate. Accordingly, the substrate can be held onto the substrate mounting surface by the Coulomb force or the Johnsen-Rahbek force.
A basic function of the electrostatic chuck is to adsorptively hold the substrate, but recently, the electrostatic chuck has generally been used for controlling a temperature of the silicon wafer during a process. By way of example, the electrostatic chuck may be used for cooling the silicon wafer by flowing an inert gas such as helium between the silicon wafer and the electrostatic chuck, or the electrostatic chuck may be used for heating the silicon wafer in combination with a heater. This is because the temperature of the substrate is closely related with a rate of an etching process or a film forming process and a quality of a processing result.
For this reason, in evaluation of the electrostatic chuck, there has been considered the temperature control function of the silicon wafer and uniformity of temperature distribution during a film forming process and an etching process onto the silicon wafer as very important evaluation factors in addition to a mechanical characteristic, a decrease of particles, improvement in purity, plasma resistance, and chemical resistance.
Generally, the temperature of the substrate during a plasma process may depend on heat inputted to the substrate or a mounting table from the outside. Therefore, the temperature control function of the substrate mounting apparatus may be influenced by heat from the outside.
Therefore, performance evaluation for the electrostatic chuck used in the plasma processing apparatus needs to consider heat inputted to the substrate or the mounting table from plasma. If a thermal condition in the performance evaluation is different from a thermal condition in an actual plasma process, results of the performance evaluation may be greatly different from results of the actual plasma process.
If characteristics of the electrostatic chuck are measured by using the plasma processing apparatus under the same condition as a process such as an actual etching process, the performance evaluation can be conducted accurately. However, it costs a lot to use a high-priced and complicated plasma processing apparatus for this evaluation. Further, there is a problem in that it takes a lot of effort and time required for the evaluation.
For this reason, disclosed in Patent Document 1 are an evaluation device and an evaluation method for an electrostatic chuck. In Patent Document 1, performance of an electrostatic chuck is evaluated by providing the electrostatic chuck in an evacuable airtight chamber and heating a substrate by a lamp heater positioned above the electrostatic chuck to simulate a thermal condition in a plasma processing apparatus.
Meanwhile, disclosed in Patent Document 2 are an evaluation device and an evaluation method for simply evaluating a substrate mounting apparatus by simulating a thermal status corresponding to an actual plasma processing apparatus.
Patent Document 1: Japanese Patent Laid-open Publication No. 2006-86301    Patent Document 2: Japanese Patent Laid-open Publication No. 2008-108938
As disclosed in Patent Document 1, the evaluation method for the electrostatic chuck is conducted in the evaluation device which simulates the thermal condition by using the lamp heater (halogen lamp) as an external heating source instead of plasma. Accordingly, the performance for the electrostatic chuck can be simply evaluated.
However, upon review of this method, the present inventor has found that it is difficult to simulate the thermal condition using plasma by the evaluation method for the electrostatic chuck disclosed in Patent Document 1.
The reason for that is a difference in a heat transfer mechanism between heat transfer from plasma and heat transfer from a conventional heating lamp or heater. Generally, it is deemed that the heat transfer from plasma of high temperature is mainly caused by contact heat transfer by molecules excited into plasma.
Meanwhile, the heat transfer from the heating lamp occurs in such a way that resonance absorption of an infrared light irradiated from a heating source occurs on a substrate, and such energy brings about motion (vibration) of molecules, and, thus, friction between vibrated materials generates heat.
Here, the infrared light irradiated from the heating lamp may mainly include a near infrared ray (about 0.78 μm to about 2 μm) and an infrared ray (about 2 μm to about 4 μm). A silicon wafer serving as the substrate mostly transmits the infrared ray (infrared light) of a wavelength in the range of from about 1 μm to about 5 μm. For this reason, the silicon wafer is hardly heated by an infrared lamp, and the infrared light penetrates the silicon wafer and entirely heats a surface (mounting surface) of the electrostatic chuck underneath the silicon wafer.
Here, in a microscopic view, there exist freaks on surfaces of the electrostatic chuck and the silicon wafer. For this reason, contact surfaces between the electrostatic chuck and the silicon wafer have some areas where the surfaces are in close contact with each other and some areas where a gap exists between the surfaces. In this status, the irradiation light (infrared light) from the infrared lamp mostly penetrates the silicon wafer. Accordingly, only the surface of the electrostatic chuck is heated at the areas where the gap exists between the surfaces, whereas the contact surface of the silicon wafer with the electrostatic chuck is heated at the areas where the surfaces are in close contact with each other. Consequently, the heat is sufficiently transferred to the silicon wafer at the areas where the surfaces are in close contact with each other. Meanwhile, the heat is not sufficiently transferred into the silicon wafer at the areas where the gap exists between the surfaces (where the surfaces are not in close contact with each other).
Meanwhile, in an actual process using plasma, it is deemed that heat is mainly transferred by contact heat transfer of molecules when molecules exited into plasma of high temperature when the molecules are brought into contact with the silicon wafer. For this reason, the entire surface of the silicon wafer can be uniformly heated.
Therefore, it is deemed that a thermal status of the electrostatic chuck and the silicon wafer in the simulation device using the infrared light is different from that in the actual plasma processing apparatus.
In order to solve this problem, disclosed in Patent Document 2 is the evaluation device for evaluating the performance of the substrate mounting apparatus by using the infrared heater as the heating source. In this evaluation device, to simulate the thermal status corresponding to the actual plasma processing apparatus, the thermal status of the plasma processing apparatus can be simply simulated by using a substrate made of silicon carbide which absorbs the infrared light instead of a substrate made of silicon.
However, the evaluation device disclosed in Patent Document 2 needs to additionally include the infrared heater or the lamp as the heating source like the evaluation device disclosed in Patent Document 1. For this reason, there is a problem in that the evaluation device becomes larger and expensive.
Further, since the heating source such as the infrared heater is positioned above the substrate, when temperature distribution of an entire substrate is measured by, for example, a non-contact radiation thermometer, the measurement may be influenced by the heating source such as the infrared heater. Meanwhile, it may be possible to use a temperature probe as a thermocouple element, but it is very difficult to arrange temperature probes as thermocouple elements on the entire substrate. If the temperature probes as thermocouple elements are arranged, areas where they are positioned have thermal characteristics that are different from other areas. For this reason, if a multiple number of such areas having thermal characteristics different from the other areas exist on the substrate for evaluation, a thermal status thereof becomes different from an actual thermal status. Accordingly, there is a problem in that performance evaluation of the electrostatic chuck cannot be simply conducted on its entire surface with high precision according to the technologies disclosed in Patent Documents 1 and 2.
Meanwhile, when a temperature control function of an electrostatic chuck serving as a substrate mounting table is evaluated, it is not necessary to uniformly evaluate an entire surface of a substrate mounting surface. According to research by the present inventor until now, it has been found that it is possible to specify some areas which should not be excluded from evaluation of characteristics of the electrostatic chuck. By way of example, there is formed a flow path for coolant used for a temperature control in the electrostatic chuck and the coolant flows into and out from the flow path. For this reason, it is difficult to control temperatures at an inlet and outlet of the coolant flow path as compared to temperatures in the other areas. Further, an area near a high voltage power supply unit where the coolant flow path cannot be formed or an area near lift pins for moving the substrate up and down have the same problem. Furthermore, an outer periphery in a circumferential direction of the substrate has a plasma density distribution problem or electric field distribution problem and needs more delicate temperature control than any other areas.
In the conventional methods, it is possible to measure and evaluate temperature characteristics on the entire surface of the substrate mounting table at a time, but it is very difficult to uniformly heat the entire substrate. Further, it costs a lot to conduct the measurement and evaluation.
With regard to this problem, the present inventor has conceived that a self-heating type evaluation substrate can be used as a dedicated substrate (hereinafter, referred to as “evaluation substrate”) to evaluate characteristics of a substrate mounting apparatus such as an electrostatic chuck. According to this, it is possible to evaluate performance of an electrostatic chuck made of, for example, silicon which transmits the infrared light. Further, if the self-heating type evaluation substrate is used, the heating source such as the infrared heater is not needed, and, thus, a non-contact thermometer can be provided thereabove. With this configuration, it is possible to measure temperature distribution of an entire surface of the evaluation substrate with high accuracy. The present inventor has derived the present disclosure in view of the foregoing description.
Accordingly, the present disclosure provides an evaluation device and an evaluation method for a substrate mounting apparatus capable of simply evaluating a temperature control function of the substrate mounting apparatus under preset evaluation conditions or circumstances, and an evaluation substrate used for the same.